1. Technical Field
The present invention relates to a fine resolution signal synthesizer that operates over a continuous frequency bandwidth using a Fractional N Delta Sum Phase Locked Loop.
2. Related Art
Traditional fine resolution synthesizers are made using one of three different techniques. The first is a Direct Synthesis technique that includes a phase locked loop that provides frequency adjustment using one of a sum, difference, multiply or a divide component. The second is a Direct Digital Synthesis (DDS) technique that creates and varies the output frequency using digital techniques. The third is a Delta Sigma approach, also know as a Fractional N Delta Sum Phase Locked Loop.
The size and power requirements for synthesizers using the first and second techniques, Direct Synthesis and DDS respectively, make those devices undesirable for use as a portable component for field testing over a desired test frequency range. The third technique, the Fractional N approach, is more ideal for creation of a portable device due to its limited size and power requirements for the same frequency range. A major drawback of this Fractional N approach, however, is a phenomenon called boundary spurs. Boundary spurs are spurious discrete frequencies that occur at particular frequency division values relative to the set time base provided in the phase locked loop. The boundary value spurs typically occur at fractional frequency values of the selected frequency division time base that approach N/4, N/2, 3N/4 and N.